1. Field of the Invention
The present invention relates to an improved safety switch for protecting circuit, and more particularly to a safety switch having a push-pull rod (coupled element) between a button shade (change-over button) and a conductive piece. The push-pull rod is formed in a collapsing manner. When the switch is overloaded, the conductive piece can be completely disconnected in order to ensure the electrical safety.
2. Description of the Prior Art
A conventional wall-mounted see-saw switch, as shown in FIG. 1, is usually used to control the On/Off of a light and which generally includes a button 11 capable of being positioned in two different positions as an exerted force is applied at one end for establishing a closed or opened circuit via a retaining tab 110 which butts against a plate 12. However, this see-saw switch must be operated manually such that the closed or opened circuit can be attained once the button is pressed at one end. Unless the button is pressed at one end, otherwise the see-saw switch will remain in a preset position, i.e. opened circuit is remained in opened position; and closed circuit is remained in closed position. This see-saw switch can not be switched from the closed position to an opened position even if an overload is encountered. If the supplied power can not be interrupted immediately, the electric conductive wires will become more and more hot, eventually, a risk of getting a fire can be encountered. In light of this, the safety and property of user can not be suitably protected.
U.S. Pat. No. 5,262,748, entitled to xe2x80x9cFuseless Breaking Switchxe2x80x9d, hereinafter referred to as ""748, has disclosed a subject matter which is intended to solve the defects of the conventional see-saw switch. This fuseless breaking switch comprises a casing 10 having a button 13 pivotally mounted thereof. The bottom of the casing 10 is further provided with three sets of prongs 15, 16, 17. One set of the prongs 17 is disposed with a contact reed 170 having a platinum conductive protrusion 171 thereof. One end of the contact reed 170 is disposed above the corresponding prong 16 and is electrically connectable with the platinum conductive protrusion 160. The button 13 is further provided with a coupled piece 14, the other end of which is in turn connected to contact reed 170. When the button 13 is depressed, the prongs 16, 17 is electrically connected via the contact reed 170 and the platinum conductive protrusion 171, 160. When the switch is overloaded, the contact reed 170 will be deformed by being heated. Accordingly, the electrical engagement of the contact reed 170 with said platinum conductive protrusion 31 is discontinued. Consequently, the supplied power is interrupted to ensure the safety and property of user.
Even the disclosure of ""748 provides an improved breaking switch to solve the problem encountered by a see-saw switch, its defects can still be concluded as follows:
1. When the button 13 is depressed or jammed, or the curved spring blade 24 experiences a fatigue, the conductive protrusion 170 will not be disconnected even in case of an overload. The breaking switch itself will be melted by the increasing heat. The potential risk of getting fire can not be suitably avoided.
2. The operating principle of the breaking switch is based as follows. When the contact reed 170 made of double alloy piece is heated during an overload and the temperature rises till the breaking temperature (normally set between 100-150 degrees Celsius), the resilience will be larger than the curved spring blade 18 such that the breaking switch is actuated to opened circuit. In this case, even if the button 21 is depressed to ON position and if the resilience of the contact reed 170 is still larger than the of curved spring blade 18, the engagement of the conductive protrusion 171 will be disconnected as soon as it is contacted. If the button 13 is kept at depressed position; even an engagement is attained between the conductive protrusions 171, 160, the contact reed 170 doesn""t work and the temperature is still increasing. On the other hand, the platinum conductive protrusions 171, 160 are contacted with each other by means of the depressing force of the user. If the force exerted thereon is not well distributed, a spark will be caused in contacting owing to load and poor contact. In this case, the platinum conductive protrusions 171, 160 will be easily oxidized and the service life will then be shortened.
3. The contact reed 170 has a planar configuration which can only be moved and deformed in one direction when experiencing an increasing heat. Accordingly, the curved spring blade 18 shall be incorporated to achieve a two-directional breaking function. The curved spring blade 18 is made from metal sheet by punching. It""s difficult to make the resilient rating of each curved spring blade 18 identical. If the rating is too high, the contact reed 170 can not be disconnected during the overload condition and the potential risk of getting fire will happen. If the rating is too low, the engagement between two adjacent platinum conductive protrusions is insufficient such that a spark will be caused. This spark will reduce the service life of the platinum conductive protrusions 171, 160.
Taiwan Pat. 334165, as shown in FIGS. 3A and 3B, discloses a change-over device of a safety switch for protecting it from the overload which is intended to remove the defects of the conventional switch. The safety switch includes a change-over button 20 having an insulting drive element 21 and an attachment element 22 at one end thereof. One end of a conductive strip 23 is clamped at one side of the attachment element 22. The insulting drive element 21 is connected with a spring 24 at one end thereof. When the switch is overloaded, the conductive strip 23 will be deformed for disconnection from the contact point so that the conductive, strip 23 together with the insulating drive element 21 are positioned by means of the insulating drive element 21 into an arched groove 25 for breaking the current loop. However, this kind of safety switch also includes the defects of the U.S. Pat. No. 5,262,748. If one of the change-over button 20, the insulating drive element 21 or the attachment element 22 is malfunction, the conductive strip 23 doesn""t work even in an overloaded situation. Besides, the spring 24 is wound by a metal wire so that it""s difficult to provide the resilience of each section thereof to be identical. The defect of too strong or too weak resilience is also present. Thus, it""s still not an excellent safety switch.
Previously, the inventor of the present invention tried to remove the above-mentioned defects with U.S. Pat. No. 5,760,672. It is characterized by means of a slight and proper jumping space (xcex94S) being created between a pushing part and a pulling part of a push-pull rod 9 (similar to the above-mentioned attachment element 22). Accordingly, when a button shade or the push-pull rod 9 is defective, an alloy plate 7 (similar to the above-mentioned conductive strip 23 or the contact reed 170) will also be deformed in a half-escape manner to be separated from the contact point 71. Therefore, the switch is situated in a disconnected state for an electrical safety. The expected effect thereof can be achieved under an ordinary conditions. However, the half-disconnection design is still not a complete structure. Since the jumping space (xcex94S) is not perfect in setting and installing aspect, the half-escape function wouldn""t work even in case of a slight carelessness.
In the above-mentioned safety switches, the attachment element (or push-pull rod) and the conductive strip (contact reed or alloy plate) are connected in a coupled state. Therefore, if one of the attachment element or the change-over button is defective, the conductive strip can""t be deformed for disconnection.
It is a primary object of the present invention to remove the above-mentioned disadvantage of the conventional safety switch and to provide a safety switch having a change-over push-pull rod between a button shade and a conductive strip. The top end of the push-pull rod is pivotally connected to the button shade while the bottom end thereof includes a pushing part and a pulling part which are not the same length. The push-pull rod and the external end of the conductive strip are not coupled, but situated in a pushing and pulling change-over relationship. In cooperation with the inner and outer spring elements and a play groove, the conductive strip will be collapsed in a manner of reverse deformation for a disconnection when the switch is overloaded, without being restricted by the pushing part and the pulling part. Besides, the safety switch includes the ON-OFF change-over function under ordinary state. The configuration is therefore simplified and the user safety is much more ensured.
It is another object of the present invention to provide a safety switch for protecting circuit which has the same effect as the conventional fuseless switch with mechanical disconnection in spite of simplification of its structure.